The invention relates to an x-ray diagnostic installation, comprising an x-ray tube having a cathode, focusing means for the electron beam, and an anode, wherein deflection means for the electron beam are present which are connected to a control circuit which is so designed that the impingement point of the electron beam on a focal region describes a predetermined path to define the effective focus shape and size.
In the operation of x-ray tubes, there is a requirement for the x-ray tube current to be very rapidly altered. Fundamentally, an alteration of the x-ray tube current by controlling the filament power is possible. However, this means of altering x-ray tube current necessitates a relatively large delay time which is not always acceptable. A very rapid alteration of the x-ray tube current is possible if a control grid is provided between the cathode and the anode of the x-ray tube. The focus must in this case have a predetermined shape and size sufficient to preclude an overloading of the anode of the x-ray tube, but not such that blurring of the x-ray image as determined by the focus dimensions becomes excessive.
From UK published patent application GB No. 2 044 489A, it is known in the case of a computer tomograph to deflect the electron beam over a region of an anode moving with the cathode about a patient such that the impingement point of the electron beam on the anode describes a predetermined scanning path. However, this path on the anode is related to a desired corresponding spacial scanning path of the x-ray beam with respect to a patient, the anode being e.g. linearly extensive to accommodate the desired scanning pattern thereon.